Lubrication device for electrostatic actuators



y 8, 1 NIYAZI AYGUN ETAL I 3,454,137

- LUBRICATION DEVICE FOR ELECTROSTATIC ACTUATORS Filed Dec. 23, 1966 IOn [lllll l-lll D S m a m m. m o N K T Y. .T EA A .V R v W M n w R T MZUnited States Patent 3,454,137 LUBRICATION DEVICE FOR ELECTROSTATICACTUATORS Niyazi Aygun and Frederick G. Krebs, Dayton, Ohio, as-

signors to The National Cash Register Company,

Dayton, Ohio, a corporation of Maryland Filed Dec. 23, 1966, Ser. No.604,331 Int. Cl. F16n 9/04 US. Cl. 184-14 1 Claim ABSTRACT OF THEDISCLOSURE A lubricating device having a lubricating stick engaging theperiphery of the drum of an electrostatic actuator employing theJohnsen-Rahbeck effect. As the drum is rotated, the stick isreciprocated along a line which is parallel to the longitudinal axis ofthe drum to trace a helical band of lubricating film on the periphery.

This invention relates to a device for lubricating the peripheries ofshafts and drums, and more specifically it relates to a lubricationdevice for electrostatic actuators of the type employing a rotating drumand an external brake band.

This type of electrostatic actuator can be used as a clutch, and, whenso used, it includes, essentially, a rotating drum and a thin metalband. The drum is coated with a highly polished layer of dielectricmaterial of high resistivity, and the metal band is wrapped around atleast a portion of the periphery of the drum, one end of the band beingfixed and the other end of the band being secured to a spring toresiliently hold the band against the drum. The drum is rotated and ischarged with a potential of one polarity. With no charge on the band,the drum continues to rotate in slipping engagement with the band;however, when the clutch is actuated, a charge of opposite polarity isplaced upon the metal band, and the band is attracted to the drum and isheld in driving engagement therewith by an electrostatic force due tothe Johnsen-Rahbeck effect. The end of the band secured to the spring ispulled in the direction of rotation of the drum to do the desired work.When the charge is removed from the metal band to deactuate the clutch,the spring restores the band to a home position in readiness for thenext cycle of operation.

Lubricating the surface of the drum in an electrostatic actuator of thetype mentioned in the previous paragraph has been a problem. Thelubrication is necessary to minimize the wear between the metal band andthe periphery of the drum, and yet the lubrication should not interferewith the driving engagement between the band and the drum. Reliableoperation of such an actuator requires a lubrication film thickness ofabout 20 to 30 microinches. Any contaminating particles in thelubrication film tend to destroy the mating surfaces of the drum and theband. If a stationary stick of lubricant is used to press against therotating drum, contaminating particles become lodged in the stick,causing excessive, uneven wear on the stick itself. Various types ofscraper cleaners and brushes were tried, but none of them provided theclean regenerative film produced by the lubrication device of thisinvention.

Applicants lubricating device includes a lubricating stick holder meanswhich is movably mounted in a frame to enable one end of the stick to bedirected at the periphery of the rotating drum. Means are also providedfor reciprocating the holder means along a line which is parallel to theaxis of the rotating drum, enabling a relatively small lubricating stickto effectively lubricate the "ice entire periphery of the rotating drum.Because the stick is being continuously moved, a surprisingly cleanlubricating film is deposited on the drum, enabling reliable operationof the electrostatic actuator. Any portions of the lubricating filmwhich are damaged by contamination particles are soon repaired by theconstant regenerative action of the moving lubrication block or stick.As the drum rotates, the lubricant stick traverses the periphery of thedrum to trace a helical band of lubricating film thereon. Successivepasses of the stick are effective to fill in the areas between adjacenthelical bands, resulting in a continuous lubricating film beingdeposited on the periphery of the drum.

Accordingly, the objects of this invention are:

(a) To provide a device for applying a thin film of lubricant to theperiphery of a rotating member and for regenerating this film;

(b) To provide a device for lubricating the mating surfaces between theperiphery of a rotating member and a mating band engaging at least aportion of said periphery and to provide a means for minimizing thewear-' ing effect of contaminating particles on said mating surfaces;

(c) To provide a device for maintaining a lubricating film of minutethickness between the mating surfaces of an electrostatic actuator asrequired for reliable operation of the actuator; and

(d) To provide a device for maintaining a lubricating film between themating surfaces of an electrostatic actuator so that variations in thefilm thickness due to the non-homogeneous character of the lubricatingstiok used to apply the film will be minimized.

These and other objects and advantages will become more readilyunderstood in connection with the following description and thedrawings, in which:

FIG. 1 is a plan view of the bottom of an electrostatic actuator,showing the means for applying a thin film of lubricant to the peripheryof the rotating member of the actuator; and

FIG. 2 is an elevational view in cross-section which is taken along theline 22 of FIG. 1, showing more details of the lubricating means of thisinvention.

The lubricating means 10 of this invention is shown in use with anelectrostatic actuator 12, of the band clutch type, which is shown inFIGS. 1 and 2. The actuator 12 is of the type which employs a rotatingsteel drum 14 supported on a shaft 16, which is supported in electricalinsulator bushing members 18 and 20 (FIG. 1). The shaft 16 is providedwith a reduced diameter portion 22, which fits into the bushing 20,which is conveniently retained in a planar support member 24. A lockingcollar 26, secured to the shaft 16 on one side of the member 24 inconjunction with the shoulder formed by the reduced diameter portion 22located on the other side of the member 24, is efiective to restrain thedrum 14 against axial movement in the planar support members 24 and 28,which are in spaced, parallel relation.

The steel drum 14, which forms a major part of the electrostaticactuator 12, has a periphery which is coated with a layer 30 of highlypolished dielectric material of high resistivity. Aside from having thedesired electrical properties to obtain the Johnsen-Rahbeck effect, thelayer 30 should also be selected to have a coeflicient of expansionsimilar to that of the metal of the drum. Historically, theJohnsen-Rahbeck effect relates to an attractive force which existswhenever a highly polished surface of metal is brought into engagementwith a similarly polished surface of lithographic stone and a potentialdilference is applied between the metal and the stone. A detaileddiscussion of the Johnsen-Rahbeck effect, with particular reference toits application to electrostatic clutches, may

3 be found in the article Electrostatic Clutches, Dudding and Losty, G.E. C. Journal, vol. 33, No. l, 1966.

The other major part of the electrostatic actuator 12 shown includes ametal band 32, which is in sliding engagement with a portion of theperiphery of the drum 14. One end of the band is fixed at 34, and theother end is secured to a spring 36, which keeps the band in slidingcontact with the periphery of the drum as it is rotated in the directionindicated by the arrow A (FIG. 2).

An electrical potential of one polarity is applied to the drum 14 via abrush 38 on the shaft 16, and, when the electrostatic device 12 is to beactuated, a potential of opposite polarity is applied to the band 32 viaa contact 40 to create the desired attractiv electrostatic force whichcauses the band 32 to be rotated with the drum 14, thereby pulling theend 42 of the band 32. When the end 42 is pulled, work can be done; thisis shown diagrammatically by the lever 44, which is pivotally mountedbetween its ends on a support 46. One end of the lever 44 is pivotallysecured to a block 48, which is secured to the end 42 of the band 32.When the potential is removed from the band 32, the band is releasedfrom the rotating drum, and the spring 36 returns the band to a homeposition in readiness for the next cycle of operation.

As previously mentioned, supplying a thin film of lubricant to theperiphery of the drum 14 of the electrostatic actuator 12 is extremelyimportant for reliable functioning of the actuator 12. The lubricatingmeans 10, shown in FIGS. 1 and 2, provides such a thin film.

The lubricating means includes a lubricant stick or block 50, which isslidably mounted in a holder 52 and is directed in a radial line towardthe axis of the drum 14. An adjustable screw 54 is used to vary thetension on a spring 56, which urges the stick 50 out of the holder 52and against the coating on the drum 14.

The holder 52 is movably mounted in the frame for reciprocating movementparallel to the axis of the drum 14, as follows. The holder 52 isprovided with a bore enabling it to be slidably mounted on a rod 58,which is parallel to the axis of the drum 14 and which rod isconventionally restrained against axial movement in the support members24 and 28. The ends of the rod 58 are mounted in conventional insulatorbushings 59 to isolate the rod and the holder 52 from the supportmembers 24 and 28. The holder 52 is also supplied with a second aperture(parallel to the first), in which a standard, reverselythreaded,transversing shaft 60 is mounted. The ends of the shaft 60 are rotatablymounted in conventional insulator bushings 62 and 64 to isolate theshaft 60 from the support members 24 and 28. A conventional pawl 66,secured to the holder 52, engages the grooves of the transversing shaft60 in the usual manner.

When the transversing shaft 60 is rotated, the holder 52 reciprocatesbetween the support members 24 and 28, enabling the small lubricatingstick 50 to also reciprocate across the periphery of the drum 14. As thedrum rotates, the reciprocating lubricant stick 50 deposits a narrowhelical band of lubricant on the periphery thereof. Upon successivepasses of the stick 50, the areas between adja cent helical bands oflubricant formed on the periphery will be filled, forming a continuousfilm thereon. Any portions of th lubricating film which are damagedeither by contaminating particles or by abrasive action between the band32 and the drum 14 are soon repaired by the constant regenerative actionof the moving lubrication stick 50. Because the shear forces acting onthe face of the lubricating stick when it is engaging the drum 14 arecomposed of components acting at right angles to each other, and becauseone of these components constantly changes direction (via thetransversing shaft), any wear particles which accumulate are kept inconstant motion, so that they do not become imbedded in the face of thestick. Temperature build-up of the stick 50 is also minimized bypreventing particles from becoming imbedded in the face of the stick 50.

The transversing shaft may be rotated independently of the shaft 16 by aseparate driving means (not shown), or the shaft 60 may be connected torotate with the shaft 16 by meshing gears 68 and 70, which are fixed torotate with the shafts 60 and 16, respectively.

The particular lubricant employed in the stick 50 is of course dependentupon the type of electrostatic actuator used, the type of dielectricmaterial used, the speed of the rotating drum, and the like. Forillustrative purposes, the coating 30 applied to the drum 14 in theembodiment shown was barium titanate applied by the flame sprayingtechnique, and the lubricant used in the stick 50 was a mixture oftetrafiuoroethylene and molybdenum disulfide.

What is claimed is:

1. A lubricating apparatus for lubricating the periphery of a rotatingmember of an actuator device of the electrostatic type, comprising:

frame means;

holder means having a lubricant stick slidably mounted therein andextending outwardly therefrom;

means for movably mounting said holder means in said frame meansenabling said lubricant stick to engage said periphery;

and means for reciprocating said holder means along a line substantiallyparallel to the axis of said rotating member as said member is rotatedto thereby lubricat said periphery;

said holder means having adjustable means to resiliently urge saidlubricant stick out of said holder means to engage said periphery;

said means for movably mounting said holder means comprising a rodmember positioned in said frame means in spaced parallel relationshipwith the axis of said rotating member;

said holder means having a hole passing therethrough to slidably receivesaid rod member, and also having a second hole in spaced parallelrelationship with said first-named hole;

saidmeans for reciprocating said holder means comprising areversely-threaded transversing shaft rotatably mounted in said framemeans in spaced parallel relationship with said rod member, saidtransversing shaft being slidably mounted in said second hole, and pawlmeans operatively connecting said holder means with said transversingshaft to reciprocate said holder means as said transversing shaft isrotated,

and connecting means operatively connecting said transversing shaft withsaid rotating member to rotate said shaft whenever said rotating memberis rotated,

said lubricating apparatus being effective to provide a clean,regenerative film of lubricant on said periphery.

References Cited UNITED STATES PATENTS 656,366 8/1900 Nelles 118242 X1,875,467 9/1932 Knoerzer et al 7457 X 2,586,014 2/1952 Dunphy 15306.1 X2,692,738 10/1954 Seaman 74-57 X 2,850,908 9/1958 Foster 19221.5 X2,923,390 2/1960 Fitch 19221.5 X

LAVERNE D. GEIGER, Primary Examiner.

EDWARD J. EARLS, Assistant Examiner.

US. Cl. X.R.

